1. Field of the Invention
The present invention relates to a wiper device for wiping off the front glass shield of an automobile and, more particularly, to an improvement in a retractable wiper device for retracting its blade below a bottom turn position.
2. Description of the Prior Art
In a retractable wiper device of this kind, there has been proposed in the prior art a wiper device (as disclosed in Japanese Utility Model Application Laid-Open No. 59-190648), as shown in FIGS. 12 to 14.
Specifically, in these Figures: reference numeral 1 designates the output shaft of a reduction gear machanism connected to a motor; numeral 2 a first crank; numeral 3 a second crank; numeral 4 a nut for fastening the output shaft 1 and the first crank 2; numeral 5 a projecting spindle projecting from the second crank 3; numeral 6 a nut for supporting the second crank 3 on the first crank 3 in a rocking manner; numerals 7 and 8 block edges formed on the first crank 2; numerals 7a and 8a recesses to engage with the second crank 3; numeral 9 a spindle fixed in the second crank 3; numeral 10 a cam fitted on the spindle 9; numeral 11 a bearing member integrated with the cam 10; numeral 12 a link; numeral 13 a bearing member at the side of the link 12; numeral 14 a wiper blade; numeral 15 an arm for supporting the wiper blade 14; numeral 16 a rocking shaft for the arm 15; numeral 17 a rocking lever associated with the link 12 and fixed to the rocking shaft 16; numeral 18 a slidable stopper mounted on the second crank 3; numeral 19 a spring for urging the stopper 18 in a direction so as to project from the second crank 3; numeral 20 a guide frame accommodating the spring 19 for guiding the same when the stopper 18 moves; and numeral 21 a mounting screw for fastening the guide frame 20 to the second crank 3.
In a ordinary wiping operation, the output shaft 1 of the motor is rotationally driven in a forward direction, as indicated by an arrow P in FIG. 14. If the first crank 2 is rotated in this direction, the second crank 3 associated through the link 12 and the rocking level 17 with the wiper arm 15 is rotated on the pivot 5 in the direction opposite to the direction P relative to the first crank 2 by the rotational reaction until it is bent to abut against the block edge 8 of the first crank 2. Simultaneously with this, the stopper 18 is introduced into the recess 7a by the urging force of the spring 19 and engaged at the bent angle. The second crank 3 is rotated on the output shaft 1 in the direction of the arrow P while being bent with respect to the first crank 2, and the rocking shaft 16 is reciprocated by the link 12 and the rocking lever 17 so that the wiping operation is carried out by the wiper blade 14.
The range for the wiper blade 14 to be reciprocated with the second crank 3 which is bent with respect to the first crank 2 is between a bottom turn position A and a top turn position C. Next, when a wiper switch (not shown) is turned off, the motor is reversed by an automatic fixed-position stop mechanism (not shown) so that the wiper arm is moved from the aforementioned position, which is taken when the wiper switch (not shown) is turned off, and is stopped at the bottom turn position A of the aforementioned operation range.
Through this reversing operation, the first crank 2 is rotated in the direction opposite to that of the arrow P. through the rotational reaction, the second crank 3 associated with the wiper blade 14 through the link 12 is rotated on the pivot 5 in the direction of the arrow P relative to the first crank 3 until it is rotated to abut against the block edge 7 of the first crank 2 and is extended. Simultaneously with this, the stopper 18 is introduced into the recess 8a by the urging force of the spring 19 to engage with the same at the extended angle.
Thus, the crank effective length when the second crank 3 is extended linearly with respect to the first crank 2, i.e., the inter-axis length joining the output shaft 1 and the spindle 9 is larger than the inter-axis length joining the output shaft 1 and the spindle 9 when the second crank 3 is bent. As a result, as shown in FIG. 14, the wiper blade 14 in the ordinary stop position (i.e., the bottom turn position) is retracted across the operation range into its retracted position B.
In the aforementioned wiping operation and blade retracting operation, the cam 10 fitted on the spindle 9 of the second crank 3 is rotated on the spindle 9 integrally with the link 12. In the forward rotations of the wiping operation, the cam 10 pushes and suppresses the stopper 18 engaging the recess 7a and leaves the stopper 18 when it rotates backward at a small angle (about 35 degrees) after the ordinary rotation (of 180 degrees). When the second crank 3 is completely extended with respect to the first crank 2, the cam 10 pushes and suppresses the stopper 18 engaging with the recess 8a.
The retractable wiper device thus constructed is enabled by a simple mechanism to retract the wiper blade from the ordinary stop position A into the retracted position B. In the forward rotation (for the wiping operation) of the motor, however, the cam 10 assumes a state in which it does not push the stopper 18, once its in its first rotation when the wiper device operates with the first crank 2 and the second crank 3 being bent at a desired angle. In this state, the binding force for inserting the stopper 18 into the recess 7a of the block edge 7 depends absolutely upon the pushing force of the spring 19 so that it is in an unstable state causing clattering or squeaking. Slight shocks are thereby caused at the leading end of the wiper blade 14 giving an unstable feel to the driver.
Therefore, I have proposed an improvement in which the aforementioned cam 10 is made to have a structure of two overlapping sheets so as to maintain the bent state of the first and second cranks 2 and 3, i.e., the state, in which the stopper 18 is fitted in the engagement recess 7a, while the first crank 2 is rotationally driven in the forward direction (as disclosed in Japanese Patent Application Laid-Open No. 61-244639).
Cam members 30 and 31 are arranged in place of the aforementioned cam 10 and are individually formed with two recesses 30a and 30b, and 31a and 31b at positions spaced at an angle .theta. of 120 degrees, as shown from (A) to (C) in FIG. 15. Moreover, the cam member 30 to be fixed on the aforementioned bearing member 11 is formed with a concentric, arcuate groove 30c which extends from the surface and to the back and has a play angle of 60 degrees, for example. The other cam member 31 is equipped with a pin 31c to be fitted in that arcuate groove 30c. As a result, during the forward rotations of the first crank 2, the arcuate face of the upper cam member 30 excepting the aforementioned recesses 30a and 30b faces the stopper 18 even if the recess 31a of the lower cam member 31 comes to a position to face the stopper 18. Thus, this stopper 18 is pushed and fixed in the engagement recess 7a so that the first and second cranks are kept in their bent states.
I have also proposed another improvement in the retractable wiper device of this kind (as disclosed in Japanese Patent Laid-Open No. 62-299452).
This proposal is intended to eliminate the drawback in the procedure for which the wiper blade 14 is operated from the retracted position B to ordinary rotation by the forward drive of the motor. Specifically, in the course of the relation between the first crank 2 and the second crank 3 to change from the linearly extended position to the bent position, the aforementioned stopper 18 comes out of the recess 8a toward the cam side. If, at this time, an external force such as an intense wind is exerted upon the wiper while the vehicle is running at a high speed, the wiper is forced upward in its rotation direction so that the cam member 30 relating to the link 12 and the rocking lever 17 is rotationally accelerated in the forward direction in addition to its ordinary rotations. Considering this acceleration, the above-specified proposal forms a relief space 36 so that the stopper 18 may be inclined around the side of the first crank 2 in the forward direction of the second crank 3, as shown in FIG. 16. Moreover, the spring 19 is arranged to keep the aforementioned stopper 18 in a predetermined position at all times. In case, with this structure, the aforementioned cam member 30 is rotationally accelerated in the forward direction, said stopper 18 is inclined into the relief space 36 against the elastic force of the spring 19. Then, the arcuate face at the outside of the cam comes into smooth contact with the trailing end face of the stopper 18 to prevent the cam member 30 and the stopper 18 from collision or hooking onto each other. As a result, the aforementioned second crank 3 continues its bending motion in this state until the stopper 18 comes to a position facing the recess 7a. According to the proposal thus far described, it is possible to effectively avoid both breakage whcih might otherwise be caused by the collision or hooking of the members and the state in which the first crank 2 and the second crank 3 might otherwise be brought to a predetermined bent angle.
The cam members 30 and 31 disclosed in the aforementioned proposal are formed with the recesses 30a and 31a having different angular apertures, as shown in FIG. 17. One cam member 30 is formed with the concentric, arcuate groove 30b having a play angle of about 180 degrees, and the other cam member 31 is formed with the bulge 31b to be fitted in the arcuate groove 30b.
In any of the proposals thus far described, while the motor is rotating backward, the extending and contracting behaviours of the crank arm are changed in accordance with the state of the wind screen (or the front glass) because the crank arm is extended and contracted by the load of the wiper (i.e., the load for the blade to wip off the glass). This phenomena will be described with reference to FIGS. 10 and 11.
FIG. 10 shows the operations where the blade is retracted from the top turn position C into the retracted position B by the backward drive of the motor. The wind screen is wet in the state shown at (A) in FIG. 10 and is dry or semi-dry in the state shown at (B) in FIG. 10.
With the wind screen being dry or semi-dry, as shown by broken lines in FIG. 11, the crank arm has its pitch changed from its bent state to its extended state, when in its retracting operation. As a result, the wiper blade has its speed dropped around the central portion of its wiping pattern so that the speed is increased to complete the retraction after the crank arm is extended. Thus, the operation feel is so bad as to raise an eyesore to the driver. Because of the aforementioned movements of the wiper blade, streaks of water droplets are left due to the change in the wiping speed of the blade, thus raising a problem of obstructing the field of vision of the driver.
With the wind screen being wet, on the other hand, the motions of the blade being retracted are smoother than those in the wet state. However, because of the low load, the shifts of the first and second cranks 2 and 3 to the extended positions may not be smooth. The position, at which the crank arm is extended, is highly dispersed to make the aforementioned more serious than when in the dry or semi-dry state.